The present invention relates to a method of synchronizing digital data during a serial-to-parallel conversion of such data. More particularly, the invention relates to a method of synchronizing digital data which is separated into data blocks, each of which comprises a group of data words and one or more synchronization words. A bit-synchronous timing or clock signal CLK is generated from the serial data stream and a word-timing signal is derived with a frequency equalling the sequential frequency of the serial words.
The German Patent No. 3 225 365 C2 discloses a method of converting serial data signals into parallel form. The signals comprise data words and synchronization words, each consisting of a number of bits. From these can be derived a timing signal T.sub.w with a frequency that equals the sequential frequency of the data words. The timing signal is employed for serial-to-parallel conversion. Since the timing signal is not specifically related chronologically to the beginnings or ends of the data words or synchronization words, the parallel data signals are initially stored in a buffer. A combinatorial circuit comprising several comparators then detects by how many bit periods the chronology of the data signals in relation to the timing signal deviates from what it should be. The parallel data signals are then obtained from the buffer in accordance with the detected deviation such that the bits belonging to each data word are simultaneously present in a prescribed distribution in the parallel signal lines.
The German Patent No. 3 718 566 A1 discloses a method of playing back data stored on magnetic tape. Serial signals detected by a playback head are initially converted from serial to parallel form without synchronizing the words, and the parallel signals are delayed one data block. The undelayed parallel signals are forwarded to a synchronization detector, and both the undelayed and the delayed parallel signals are supplied to a multiple-switching device. The synchronization detector generates synchronization information specifying by how many timing periods the serial-to-parallel conversion deviates from word-synchronized serial-to-parallel conversion when data information and word synchronization are recognized as identical. The synchronization information is stored in a register and utilized to control the multiple-switching device.
The publication "Standard of Recording Digital Television Signals on Magnetic Tape in Cassettes", of the European Broadcasting Union (EBU), Tech. 3252-E, describes synchronizing with the 16-bit hexadecimal synchronization word 30F5 (0011000011110101.sub.bin). When the approach described in the German Patent No. 3 718 566 A1 is employed, two such 30F5's must be detected one data block apart for the data bits between the synchronization words to be emitted in the capacity of a block to use for further data processing. When, however, a data signal recorded in accordance with the aforesaid EBU standard exhibits a higher rate of error during playback, the prescribed synchronization-bit sequence of 30F5's will be contaminated by bit errors, and detection of the synchronization words in the reproduced data signal will fail even when there is a correctable data block between the contaminated synchronization words.
Synchronization can be improved, for example, by allowing a defective bit in the synchronization-bit sequence of the 16-bit synchronization word 30F5. One bit error per synchronization word would accordingly no longer affect synchronization, and the improved yield of data blocks would on the whole be expected to lead to a lower error rate. Such an approach would also, of course, increase the probability of faulty synchronization due to faulty-synchronization words in the flow of the played-back data signal. Instead of one word, 16 additional words can be taken for synchronization words. Although the synchronization words must occur an exact distance from the data blocks, thus reducing the potential for faulty synchronization, certain image patterns can lead to increased faulty synchronization values.